Absolute concentration measurements of C 2 in a diamond CVD reactor by laser-induced fluorescence

By use of Laser-Induced Fluorescence (LIF) the absolute concentration of the C₂ radical in a microwave excited diamond chemical vapour deposition plasma has been measured for the first time. LIF spectra of the (1, 0) Swan band near 473 nm were recorded and synthesized theoretically allowing the plasma temperature of 2100 +_ 200 K to be inferred. Quenching rates were determined from time-resolved measurements of the fluorescence decay. By calibrating the LIF detection system, using spontaneous Raman scattering in H₂ in the reactor vessel, the absolute concentration of C₂ was determined to be (7.5⁺_-1.7) x 10¹⁰ cm^-3. Observations of the C₂ density under varying plasma conditions are reported.